Such apparatus for hydrogenating gasification, for instance, is described in German Published Prosecuted Application No. 2 609 320. There, the coal is heated with hot hydrogen for coal gasification counterflow-wise in a reaction vessel to above 700.degree. K. and is partly gasified in the process. The raw material particles in the reaction vessel have a tendency to adhere or cake. To reduce this tendency, oxygen may be added to effect partial combustion of the raw material. This destroys raw materials and also introduces extraneous combustion products in the reaction products. A fluidized bed has been suggested to minimize adhesion or caking of the particles, but this involves more complicated and costly apparatus and operation.